Considerable safety measures are required when drilling for oil and gas on-shore and off-shore, and one of the key safety measures is the use of blowout preventers. BOPs are basically large valves that close, isolate and seal the wellbore to prevent the discharge of pressurized oil and gas from the well during a kick or other event. One type of BOP used extensively is a ram-type BOP. This type of BOP uses two opposing rams that close by moving together to either close around the pipe or to cut through the pipe and seal the wellbore.
The blowout preventers are typically operated using pressurized hydraulic fluid to control the position of the rams. Most BOPs are coupled to a fluid pump or another source of pressurized hydraulic fluid. In most applications, multiple BOPs are combined to form a BOP stack, and this may include the use of multiple types of BOPs. In some applications, several hundred gallons of pressurized hydraulic fluid may have to be stored at the BOP to be able to operate the BOP.
U.S. Pat. No. 7,338,027 describes a ram-type blowout preventer that is designed to use less fluid to address the problems of storing and pressurizing large quantities of hydraulic fluid. The patent provides an overview of a BOP and the method of its operation.
Conventional hydraulic blowout preventers require a considerable amount of space, mainly due to the hydraulic storage tanks and the associated pressurized accumulators that are used as the driving force for the hydraulic fluid. Further, these systems are heavy and become more difficult to operate and less efficient when used in deepwater subsea conditions because of the hydrostatic pressure of the seawater. In addition, hydraulic blowout preventers can take some time to close depending on the control scheme being used to close the blowout preventer. It is desirable to provide a blowout preventer that does not have these disadvantages.